1. Field of the Invention
The present invention relates to an edge correction apparatus, and more particularly, to an improved apparatus for and a method of effectively correcting an edge of an image signal in horizontal, vertical and diagonal directions.
2. Description of the Related Art
An image signal, which is reproduced by a recording and reproducing apparatus, transmitted via a cable, or taken by a television camera, is prone to losing its high-frequency component when passing through a total transmission band such as a transmission and/or recording fields. Especially, in this case, edges of an image corresponding to the image signal become unclear, and a sharpness of the image is lowered. This triggers a need to improve a quality of an image.
Also, a method of enhancing the quality of the image is required to clearly reproduce the image signal of a limited definition, e.g., a television signal or a VTR signal, and display the image on a display apparatus, such as a plasma display panel (PDP) or a projection TV that is getting bigger and bigger in size.
In order to enhance the quality of the image signal, a general edge correction apparatus enhances the definition of the edges of the image signal by obtaining a differential signal from the image signal and adding the differential signal to the image signal. However, although the general edge correction apparatus performs the edge correction on the image signal in vertical and horizontal directions, an edge of the image signal in a diagonal direction is not corrected. Therefore, it is impossible to enhance the overall definition of the image.
FIG. 1 is a block diagram of a conventional edge correction apparatus. This edge correction apparatus includes a delayer 102, a first differentiator 104, an absolute value calculator 106, a second differentiator 108, first and second multipliers 110 and 112, and an adder 114.
The edge correction apparatus of FIG. 1 corrects edges of an image signal by obtaining a second differential signal and adding it to the image signal. At this time, the delayer 102 is used to compensate for time delays in obtaining the second differential signal.
The edge correction apparatus of FIG. 1 corrects the edges of the image signal in a horizontal direction by correcting a horizontal component of the image signal, and corrects edges of the image signal in the vertical direction by correcting a vertical component of the image signal.
When the image signal is input to the edge correction apparatus of FIG. 1, the input image signal is differentiated in the first differentiator 104 to generate a first differential signal. Then, the first differential signal is applied to the second differentiator 108 to generate a second differential signal.
Meanwhile, the first differential signal is transmitted to the absolute value calculator 106 to obtain its absolute value. An absolute value of the absolute value calculator 106 and the second differential signal output from the second differentiator 108 are combined in the first multiplier 110. An output of the first multiplier 110 is transmitted to the second multiplier 112. Then, the second multiplier 112 amplifies the output of the first multiplier 110 according to a predetermined gain. An output of the second multiplier 112 is transmitted to the adder 114.
The adder 114 is also given the input image signal delayed by the delayer 102. Thus, the delayed input image signal and a combination of the first and second differential signals that are differentiated from the input image signal are inputted to the adder 114.
FIGS. 2A–2E are waveform diagrams illustrating an operation of the edge correction apparatus of FIG. 1. Referring to FIGS. 2A–2E, a signal A is the input image signal having a rising component. Here, the rising component of the input image signal is formed at an edge of the image signal, e.g., on a border between dark and bright sides in an image.
In FIG. 2B, a signal B is an absolute value of the first differential signal obtained by first differentiating the signal A. In FIG. 2C, a signal C is a second differential signal that is differentiated from the signal B, that is, a signal that is differentiated two times from the signal A. In FIG. 2D, a signal D is obtained by multiplying the first differential signal, i.e., the signal B, by the second differential signal, i.e., the signal C, in the first multiplier 110. In FIG. 2D, a signal E is obtained by adjusting a gain of the signal D by the second multiplier 112. In FIG. 2E, a signal F is obtained by adding the signals A and D by the adder 114, and a signal G is obtained by adding signals A and E by the adder 114. A comparison of signals F and G shows that the edges of the image signal are corrected by adjusting the gain applied to the second multiplier 112.
However, the edge correction apparatus of FIG. 1 is disadvantageous in that it can be applied to correct the edge of an image signal only in the vertical and horizontal directions, but the edge of the image signal in a diagonal direction is not corrected. Therefore, it is difficult to enhance the overall definition of the image signal with this edge correction apparatus.